The growth and survival of some types of cancer cells are known to be influenced by hormones which activate hormone receptors on/in target cells. For example, breast cancer cells have been shown to be highly dependent upon estrogen for proliferation and/or survival. Estrogen is thought to impact cell growth by binding to and activating the estrogen receptor (ER), a member of a large family of transcriptional regulators (reference herein to the “estrogen receptor” is meant to refer to all estrogen receptors). After binding of the estrogen ligand, the estrogen receptor is activated through phosphorylation and receptor dimerization. Activated ER regulates the transcription of a number of genes important to controlling cellular fate through its ability to bind estrogen response elements in the promoters of target genes and impact gene transcription (see, e.g., Osborne, et. al., J. Natl. Cancer Inst. 85, 1917-20 (1993), incorporated herein by reference in its entirety). The resulting changes in the transcriptional profile can impact, potentially, both the cell with the activated ER as well as neighboring cells.
The development of prostate cancer is also highly dependent on the activation of hormone receptors by androgens, e.g., dihydroxytestosterone. (Schiff & Osborne, Breast Cancer Res. 7, 205-211 (2005), incorporated herein by reference in its entirety). The prostate produces dihydroxytestosterone from testosterone through the action of 5-alpha-reductase. In the cytosol, dihydroxytestosterone binds to and activates the androgen receptor (reference herein to the “androgen receptor” is meant to refer to all androgen receptors). As in the case of the activated estrogen receptor, the activated androgen receptor can bind androgen response elements, thereby influencing gene expression and triggering cell proliferation.
Because of the dependence of tumor cell growth and survival on activated hormone receptors, hormone therapy treatments, also known as endocrine therapy treatments, have been developed that target these receptors in various ways. Both breast and prostate cancer frequently express these receptors and, thus, are susceptible to targeting of either the hormone receptors or the production of the hormone responsible for binding and activating the receptors (for example, estrogens and androgens) (Schiff & Osborne, Breast Cancer Res. 7, 205-211 (2005); Hynes & Lane, Natl. Rev. Cancer, 5, 341-45 (2005), each of which is incorporated herein by reference in their entireties). Such hormone therapies usually target either the receptors directly or lower the production of hormones which bind to and activate these receptors, thereby reducing mitogenic and/or survival signaling from the receptors.
While hormone therapy can be initially useful in reducing tumor growth or shrinking tumors, many patients do not respond to such therapy and those that do respond eventually become resistant to treatment. Such resistance often results despite the availability of different classes of hormone therapy treatments, and cross-resistance is not uncommon.
Resistance to hormone therapy is consistent with intrinsic or acquired activation of alternative signaling pathways sufficient to support tumor cell survival. Significant evidence implicates the ErbB pathway as playing some role in resistance to hormone therapy.
The ErbB receptors (also known as the EGF family of receptors) are a subclass of the receptor tyrosine kinase (RTK) family and include four members: 1) HER-1, also known as the epidermal growth factor receptor (EGFR); 2) HER-2, also known as erbB2, c-neu, or p185; 3) HER-3, also known as erbB3; and 4) HER-4, also known as erbB4. The biological consequence of ErbB receptor signaling is frequently associated with cellular differentiation, growth or survival. EGFR, HER-2, and HER-3 have been implicated in reduced clinical responsiveness to hormone therapy.
For instance, evidence supports the idea that EGFR activation may be sufficient, or at least contribute to estrogen independence and/or resistance to hormone therapy in breast cancer. For example, selection for resistance to the aromatase inhibitor, letrozole, in an estrogen dependent cell line resulted in concomitant activation of the EGFR pathway and sensitization to EGFR kinase inhibition (Sabnis, et. al., Cancer Res. 65, 3903-10 (2005), incorporated herein by reference in its entirety). Additionally, enforced expression of EGFR in multiple tamoxifen sensitive breast cancer cell lines resulted in estrogen independence and/or resistance to hormone therapy (Van Agthoven, et. al., Cancer Res. 52, 5082-88 (1992); Miller, et. al., Cell Growth Differ. 5, 1263-74 (1994), each of which are incorporated herein by reference in their entireties). Conversely, inhibition of EGFR signaling can restore responsiveness to hormone therapy (Kurokawa & Arteaga, Clin. Cancer Res. 7, 4436s-42s, 4411s-4412s (2001), incorporated herein by reference in its entirety).
Signaling from EGFR may also play a role in reducing the efficacy of hormone therapy for the treatment of non-small cell lung cancer (NSCLC) patients. For example, inhibition of the EGFR tyrosine kinase increased the anti-tumor activity when used in combination with the hormone therapy agent, fluvestrant, an estrogen receptor downregulator (Stabile, et. al. Cancer Res. 65, 1459-70 (2005), incorporated herein by reference in its entirety). This suggests that signaling from activated EGFR may decrease the effectiveness of hormone therapy treatments in NSCLC as well.
HER-2 has also been implicated in resistance to hormone therapy for breast cancer patients. For example, activation of HER-2 has been correlated with reduced clinical responsiveness to hormone therapy (Kurokawa & Arteaga, Clin. Cancer Res. 7, 4436s-42s, 4411s-4412s (2001); Wright, et. al. Cancer Res. 49, 2087-90 (1989), each of which is incorporated herein by reference in their entireties). Indeed, HER-2 expression is sufficient to convey anti-estrogen resistance (Benz, et. al., Breast Cancer Res. Treat. 24, 85-95 (1993), incorporated herein by reference in its entirety).
HER-2, as well as HER-3, also appears to be involved in the onset of hormone resistance in prostate cancer patients. Approximately, one-third of prostate cancer patients receive hormone therapy treatment aimed at disrupting the action of testicular and adrenal androgens. As with breast cancer, resistance is inevitable. Recent data suggests that signals emanating from HER-2 and HER-3 induce a “hormone-refractory” state (Mellinghoff, et. al., Cancer Cell 6, 517-27 (2004), incorporated herein by reference in its entirety).
In summary, substantial evidence suggests that signaling from ErbB receptors plays some role in reducing the clinical responsiveness to hormone therapy in several different types of cancer, as well as contributing to the development of resistance to hormone therapy. Accordingly, one approach to increasing clinical responsiveness to hormone therapy and limiting the development of resistance in patients is to reduce the mitogenic and survival signals from the ErbB family of receptors. Signaling from the ErbB receptors is a complex process, but an important step is activation of the ErbB receptors.
Signaling by the ErbB family of receptors is thought to be initiated by ligand binding which triggers homo- or hetero-receptor dimerization, reciprocal tyrosine phosphorylation of the cytoplasmic tails, and activation of intracellular signal transduction pathways. The availability of signalling competent ErbB ligands which bind to and activate the ErbB receptors is mediated by various metalloproteases. For example, the ADAM (A Disintegrin And Metalloprotease) family of zinc-dependent metalloproteases has been demonstrated to catalyze cell surface ectodomain shedding of specific proteins (Moss and Lambert, Essays in Biochemistry 38:141-153 (2002); Chang and Werb, Trends in Cell Biology 11:537-543 (2001); Seals and Courtneidge, Genes and Development 17:7-30 (2003), each of which is incorporated herein by reference in their entireties). Specifically, the ADAM family has been shown to cleave ligands responsible for activating the ErbB receptors (Blobel, Nat. Rev. Mol. Cell. Biol. 6, 32-43 (2005), incorporated herein by reference in their entireties). For example, ADAM10 has been demonstrated to cleave proteins such as APP and Notch as well as other cell surface proteins. It is particularly important to note that ADAM 10 can cleave the extracellular domain of heparin-binding epidermal growth factor-like growth factor (HB-EGF). This cleavage process leads to the generation of a soluble fragment of HB-EGF that can bind to and activate EGFR (HER-1). Hence, one approach to decrease signaling from the ErbB receptors, such as EGFR, would be to inhibit the metalloproteases responsible for the cleavage of the ErbB ligands, such as the extracellular domain of HB-EGF.
Additionally, the ADAM10 and ADAM 15 metalloproteases have been shown to cleave the extracellular domain (ECD) of the HER-2 receptor to yield a truncated, membrane-associated receptor (sometimes referred to as a “stub” and also known as p95), and a soluble extracellular domain (also known as ECD, ECD105, or p105). This activity of ADAM10 and ADAM15 was shown in U.S. Patent Appl. No. 2004/0247602, which is incorporated herein by reference in its entirety. As with other EGF receptor family members, loss of the extracellular ligand binding domain renders the HER-2 intracellular membrane-associated domain a constitutively active tyrosine kinase. It has therefore been postulated that cleavage of the ECD of HER-2 creates a constitutively active receptor that can directly deliver growth and survival signals to the cancer cell. Furthermore, the truncated form of HER-2 receptor (p95) has been shown to interact with and activate signaling through EGFR (HER-1). Hence, another approach to decreasing signaling from both HER-2 and EGFR would be to inhibit formation of the truncated HER-2 receptor (p95).
Additionally, high levels of circulating HER-2 ECD in breast cancer patients has been correlated with reduced response rates to multiple hormone therapies and overall poor prognosis (Lipton, et. al., J. Clin. Oncol. 21, 1967-72 (2003); Carney, et. al. Clin. Chem. 49, 1579-98 (2003), each of which is incorporated herein by reference in their entireties). Hence, another approach to reducing the signaling from the ErbB receptors would be to reduce the formation of HER-2 ECD.
Nonresponsiveness and resistance to hormone therapy continue to present significant roadblocks to the successful treatment of cancer patients with hormone therapy. Accordingly there is an acute need to develop methods and compositions that increase the clinical responsiveness to hormone therapy and that inhibit or stop the development of resistance in patients. This invention addresses these needs and others.